The present invention relates generally to methods and apparatus for treating or controlling medical, psychiatric or neurological disorders by application of modulating electrical signals to a selected nerve or nerve bundle of the patient, and more particularly to techniques for treating comatose patients by application of signals to a preselected cranial nerve, specifically the vagus nerve, using an implanted neurostimulating device.
Coma may be defined as a state of profound unconsciousness from which the patient cannot be roused by ordinary treatment. The name is derived from the Greek word koma, which means deep sleep, but in fact coma is not sleep at all, but a state of unconsciousness usually caused by injury or illness. In general, unlike patients who experience even very deep sleep such as in narcolepsy (sudden uncontrollable sleep attacks and cataplexy, often accompanied by visual or auditory hallucinations at the onset of sleep), the comatose patient displays no spontaneous eye movement, nor response to painful stimuli (in deep stages of coma), nor ability to speak. There are, however, degrees of conscious impairment in patients which may not rise to the level of coma, as measured by the Glasgow coma scale. Under that scale, in which best motor response, best verbal response, and minimum stimulus to cause eye opening are tested and scored, the scores may range from 3 to 15. A score of 3 indicates no motor response (regardless of cause), no vocalization even in response to noxious stimulus, and no eye opening in response to noxious stimuli. Scores of 7 or less on the Glasgow scale qualify as coma.
It will be appreciated that coma is not a single uniform disorder, but may stem from different causes such as trauma, disease, toxic condition or other condition, and which may be characterized by different levels of consciousness. It is a principal object of the present invention to provide new and improved methods for treating patients suffering degrees of conscious impairment constituting coma, regardless of cause of the coma.